Slope

A quantity which gives the inclination of a curve or line with respect to another curve or line. For a Line in the Plane making an Angle $\theta$ with the x-Axis, the Slope $m$ is a constant given by

$$m \equiv {\Delta y\over \Delta x}= \tan\theta,$$

where $\Delta x$ and $\Delta y$ are changes in the two coordinates over some distance. It is meaningless to talk about the slope in 3-D unless the slope with respect to what is specified.